A reinforcing agent for sidewalk and treads of tires is generally carbon black. Carbon black is a conductive substance. Sidewalls and treads including carbon black are excellent in conductivity. Static electricity generated at a vehicle is discharged to a road surface via a rim, sidewalls, and a tread.
Instead of carbon black or together with carbon black, silica may be blended in a tread. By blending silica, a tire having reduced roiling resistance can be obtained. Silica is a non-conductive substance. A tire of which a tread includes silica is poor in conductivity. A vehicle on which the tire is mounted is easily charged with static electricity. The static electricity causes radio noise. In addition, the static electricity provides a feeling of discomfort to a driver by sparks.
JP9-266280 (JP No. 3364511) discloses a tire including a terminal portion. The terminal portion is formed integrally with an under tread. The terminal portion penetrates through a tread and is exposed on a tread surface. Static electricity is discharged to a road surface via a rim, sidewalls, the under tread, and the terminal portion.